This invention is related to apparatus for conducting corrosion tests on various materials, and in particular, it is directed to improved apparatus for positioning and shielding sensor probes used to control atmosphere within a corrosion test chamber.
It is well known in the art of corrosion testing that test chambers are equipped with humidity probes to monitor and control relative humidity within the chamber. Such humidity probes are often problematic because they are fixed-in-place within the test chamber where they are continuously exposed to high humidity and salt fog or spray that is used to determine the corrosion resistance of various materials. Current state-of-the-art sensor probes are unable to withstand the affects of such hostile environments. Salt spray deposits from the fog buildup on the sensor probes can cause complete probe failure. In such instances, probe replacement is necessary to continue testing. The probes can also become wet from the high humidity inside the test chamber, up to 100% relative humidity. In this instance, the wet probe will either fail to send signals, or send unreliable signals to the chamber controller. Such wet probes must be removed from the test chamber for complete drying and cleaning to make them suitable for reuse. Accordingly, service life for past corrosion test humidity probe devices has been short, and the necessary maintenance to maintain such probes in a clean and dry reliable condition interrupts corrosion testing.
In the past, there have been attempts to overcome the aforementioned sensor probe problems. For example, in U.S. Pat. No. 4,794,804, Ishii teaches that corrosion test salt spray " . . . adheres to the humidity sensor provided in the test chamber, making it impossible to perform humidity measurements." Ishii attempts to solve this problem by using a probe shield that includes a box like probe container having a hinged lid that covers a humidity probe positioned within the container. The probe container is attached to an inside wall of the test chamber, and the fixed-in-place humidity probe is shielded from or exposed to test chamber environment by either rotating the hinged lid to a closed position or rotating the hinged lid to an open position. However, when Ishii rotates his lid to an open position, the interior of his box is exposed to whatever condition may exist within the test chamber. His open lid greatly increases the chance for residual salt and moisture to enter and adhere to the inside surfaces of his box, and this increases the likelihood for sensor contamination and failure.
Another attempt to improve sensor probe reliability is disclosed in an undated drawing labeled Exhibit A listed on PTO-FORM 1449 of the instant application. The probe arrangement shown in the drawing was designed by Atotech USA Inc., during the 1980's when Atotech was known as The Harshaw Chemical Company. Atotech has disclosed that during about the year 1987, a single probe device, as shown in Exhibit A, was built and sold to a Harshaw customer. No subsequent probes or sales were ever made after that first sale date.
As disclosed by Atotech, and referring to Exhibit A, the Harshaw drawing shows a probe assembly 1 attached to a test chamber wall 2 and a drive 3 to extend or retract a sensor probe 4 relative to the inside space 5 of the chamber. The probe assembly includes a first PVC pipe 6 attached to and extending through the chamber wall 2 and a second concentric PVC pipe 7 moveably mounted within pipe 6. Drive 3 is attached to pipe 7 via a mounting plate 8 to move pipe 6 toward or away from the inside space 5 of the chamber, and the sensor probe 4 is fixed to plate 8 to follow the movement of the pipe. The sensor probe extends along the inside length of both pipes and is spaced apart from the inside walls 6a and 7a of pipes to prevent unnecessary contact with the delicate sensor prove surface. The Harshaw arrangement enables operators to insert or remove the sensor tip 9 with respect to chamber space 5. However, when the sensor tip is inserted into chamber space 5, to monitor chamber conditions, seal plate 10 is moved away from pipe 6 to expose the inside diameter 6a to the atmosphere within the chamber. This condition is similar to Ishii where the inside surfaces are now open to contamination by residual salt and moisture from the chamber and possible probe failure.
Such probe shielding devices of the past have failed to provide adequate protection against hostile environment within a corrosion test chamber, and such shielded probes continue to be prone to premature failure and short service life. For example, referring again to Ishii's humidity probe arrangement, the probe arrangement fails to provide any means for removing the humidity probe from the corrosion test chamber when the chamber environment is not being monitored by the probe, for instance during salt fogging cycles. And even though the humidity probe is shielded within the container, at such times, the humidity probe is still exposed to the high humidity produced during salt fogging, about 100% relative humidity. High humidity can cause condensation to form on the sensitive probe tip housed within the container, and the wet probe tip will produce faulty signals to the chamber controller during the next chamber monitoring cycle. Ishii's humidity probe can also be exposed to small amounts of salt water that seep into the container during a salt fogging cycle, or to salt water that drips onto the probe when the wet lid is rotated to an open position after fogging. Consequently, such condensation and salt buildup will cause the probe to either completely fail or send unreliable signals to the chamber controller. Again, such conditions make it necessary to discontinue the corrosion test activity to remove the contaminated probe from the chamber for either drying, cleaning, or replacement of the probe.